Device for defecting a magnetic field, magnetic field measure and current meter

ABSTRACT

A device for detecting a magnetic field, e.g., a magnetic field meter and an ammeter are described, the device having a first lateral magnetotransistor and a second lateral magnetotransistor, and in which the first and the second lateral magnetotransistors are complementary.

FIELD OF THE INVENTION

The present invention relates to a device for detecting a magneticfield, and particularly relates to a magnetic field meter and anammeter.

BACKGROUND INFORMATION

The number and range of applications for magnetic field sensors isgrowing steadily, in the automotive industry in particular. Among otherthings, magnetic field measurement may be used for the non-contact,low-loss, and potential-free measurement of currents. Examples includethe determination of electrical operating parameters of generators andelectrical drives. In general, currents from the milliampere to thekiloampere range must be measured, which requires a measuring range offive to six orders of magnitude.

The devices known today measure magnetic fields of current conductors,for example, by using magnetic field sensors such as Hall sensors,bipolar magnetotransistors, magnetoresistive resistors, lateralmagneto-FET structures, etc. A particularly sensitive component is thelateral magnetotransistor, the function of which is based on theasymmetrical current distribution generated by the magnetic fieldbetween two bipolar transistors.

For currents in the milliampere range, even such components reach thelimits of their sensitivity due to the low magnetic fields, typically inthe μT range. For that reason, in the related art, low magnetic fieldsare amplified by flux concentrators which make the magnetic fieldsstronger at the site of the magnetic field sensors through suitableshaping of the current conductors or through magnetic circuits made ofhighly permeable materials.

SUMMARY OF THE INVENTION

The device according to the present invention for detecting a magneticfield, the magnetic field meter of the present invention and the ammeteraccording to the present invention do not require the use of fluxconcentrating devices, which saves costs and reduces the spacerequirements. This is made possible by increasing the sensitivity of thedevice of the present invention. In doing so, the linear relationshipbetween the measuring signal and the magnetic field to be measured islargely preserved.

In one aspect, the present invention relates to a device for detecting amagnetic field, a magnetic field meter, and an ammeter that consist oflateral magnetotransistors that are complementary in that the firstlateral magnetotransistor is of the npn type and the second lateralmagnetotransistor is of the pnp type. This makes it possible to providetwo complementary lateral magnetotransistors by simple means. As aresult, the complementary lateral magnetotransistors may also be usedfor an automatic offset compensation or temperature compensation.

In another aspect, the present invention relates to a device fordetecting a magnetic field, a magnetic field meter, and an ammeter thatconsist of a first lateral magnetotransistor that has a first output anda second output, a second lateral magnetotransistor that has a third anda fourth output, and in which the first and third outputs are connectedusing low resistance, the second and the fourth outputs are connectedusing low resistance and a measuring bridge is provided between thefirst and the fourth outputs. This makes it possible to pick off avoltage or a current across the measuring bridge directly on thesemiconductor chip, on which the lateral magnetotransistors areimplemented without the need for additional shunt resistors or anexternal circuit. The signal-to-noise ratio is thus improved compared toan LMT sensor having a single lateral magnetotransistor. The measuringbridge is highly sensitive and may therefore be adjusted veryaccurately, for example, by a zero adjustment without an externalmagnetic field. In addition, the measuring bridge balancing, e.g.,offset compensation, may be performed very simply, for example, viaslight changes in the working point of one of the lateralmagnetotransistors involved. Temperature drifts may be similarlycompensated.

In another aspect, the present invention relates to a device fordetecting a magnetic field, a magnetic field meter, and an ammeter inwhich the lateral magnetotransistors are monolithically integrated. As aresult, it is possible to implement the complementary lateralmagnetotransistor sensor arrangement on one chip, resulting in a highlysensitive sensor element. In addition, this also makes it possible toprovide an evaluation circuit on the chip which is used to amplify themeasuring bridge signal. In addition, the implementation of thecomplementary lateral magnetotransistors requires no substantialadditional expense in production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a lateral magnetotransistor.

FIG. 2 shows a schematic equivalent circuit diagram for a combination oftwo complementary lateral magnetotransistors having a bridgearrangement.

FIG. 3 shows simplified equivalent circuit diagram for the bridgearrangement.

DETAILED DESCRIPTION OF THE INVENTION

A lateral magnetotransistor 1 is shown in FIG. 1. Lateralmagnetotransistor 1 is also abbreviated as LMT 1. LMT 1 includes a firstsemiconductor substrate layer 5 which is negatively doped in an npn typeLMT. In addition, LMT 1 has a second semiconductor substrate layer 6which is positively doped for the npn type. A first metal plating layer7 is provided beneath first semiconductor substrate layer 5 for bonding.First metal plating layer 7 forms the vertical collector of LMT 1. Afirst semiconductor substrate area 8 is embedded in second semiconductorsubstrate layer 6, the semiconductor substrate area being negativelydoped in the npn type and positively doped in the pnp type. In addition,a second semiconductor substrate area 9 is embedded adjacent to firstsemiconductor substrate area 8 and a third semiconductor substrate area10 is embedded in second semiconductor substrate layer 6, firstsemiconductor area 8 being situated in the middle between semiconductorsubstrate area 9 and third semiconductor substrate area 10. Second andthird semiconductor substrate areas 9, 10 are also doped like firstsemiconductor substrate area 8. A first metallic bonding 20 is situatedabove second semiconductor substrate area 8, the first metallic bondingforming the emitter contact of LMT 1. A second metallic bonding 30 isprovided above second semiconductor substrate area 9, the secondmetallic bonding forming a first collector of the LMT. A third metallicbonding 40 is provided above third semiconductor substrate are 10, thethird metallic bonding forming a second collector of LMT 1. In additionto second metallic bonding 30, a fourth metallic bonding 50 is locatedon the side opposite first metallic bonding 20, the fourth metallicbonding forming a first base terminal of LMT 1. In addition to thirdmetallic bonding 40, a fifth metallic bonding 60 is located oppositefirst metallic bonding 20, the fifth metallic bonding forming a secondbase terminal of LMT 1.

FIG. 1 shows the current directions of various currents that flow whenan npn type LMT 1 is operated. For a pnp type, the current directionswill be reversed. In npn type LMT 1, a first current 11 flows verticallydownwards from emitter area 8, i.e., from first semiconductor substratearea 8. First current 11 corresponds to the input current of LMT 1,which is fed via emitter terminal 20. During operation, collectorterminals 30, 40 are connected to the same potential and a secondcurrent 12 flows from emitter area 8 to second collector area 9, i.e.,to second semiconductor substrate area 9 and in addition, a thirdcurrent 13 flows from emitter area 8 to third collector area 10, i.e.,to third semiconductor substrate area 10. In the absence of a magneticfield 14, second current 12 and third current 13 are of equal magnitude.In the presence of a magnetic field 14 having a component pointingvertically into the plane of the illustration, which is suggested by across in magnetic field 14, first and second currents 12, 13 areunbalanced: one of the currents becomes larger.

A schematic equivalent circuit diagram of a combination of twocomplementary LMT elements is shown in FIG. 2. A first LMT 1 is of thenpn type and a second LMT 2 is of the pnp type. First LMT 1 has thereference symbols known from FIG. 1, the emitter being 20, the firstbase terminal 50 and the second base terminal 60, the first collectorterminal 30 and the second collector terminal 40. Second LMT 2 has acomplementary structure that, according to the present invention, is ofa pnp type in particular. Second LMT 2 therefore has an emitter 21, afirst base terminal 51 and a second base terminal 61 as well as a firstcollector 31 and a second collector 41. First LMT 1 has a first outputand a second output and second LMT 2 has a third output and a fourthoutput. According the present invention, first collector 30 of first LMT1 forms the first output; furthermore, second collector 40 of first LMT1 forms the second output; furthermore, first collector 31 of second LMT2 forms the third output and second collector 41 of second LMT 2 formsthe fourth output. The first two collectors 30, 31 of the two LMTs 1, 2are connected using low resistance, which means that the first and thethird outputs are connected using low resistance. In addition, the twocollectors 40, 41 of LMTs 1, 2 are connected using low resistance, whichmeans that the second and fourth outputs are connected using lowresistance. In addition, the first output and the fourth output (orconversely) as well as the second output and the third output areconnected to each other by a measuring bridge 80. Vertical collector 7of LMT 1 is not shown in FIG. 2 because it is not absolutely needed forthe description of the circuit's function or for the basic LMT function.

The four emitter-collector resistors of the two LMT elements 1, 2 form ameasuring bridge, which is balanced, for example, without an externalmagnetic field 14. In this configuration, any change due to the presenceof a magnetic field may be determined very precisely.

In principle, it is possible to assemble the circuit from discretecomponents. In one embodiment, the device according to the presentinvention implements the complementary LMT arrangement on a single chip.A feature of the present invention is that it is possible to pick offthe signal either as a current or as a voltage using the measuringbridge. A conventional LMT sensor according to the related art generallyrequires external resistors at the output of the lateral collectors inorder to measure the voltage drop of the collector currents and todetermine the changes induced by the magnetic field from it. Theconsequences are generally a deterioration of the signal-to-noise ratiodue to the external circuit, caused, for example, by the thermal noise.In a complementary LMT sensor chip, it is possible to avoid theseeffects using the measuring signal which is directly available at bridge80. Therefore, not only is the sensitivity higher but thesignal-to-noise ratio is better than in an individual LMT element.

An extremely simplified equivalent circuit diagram for the bridgearrangement is shown in FIG. 3. The resistor between emitter terminal 20and first collector terminal 30 of first LMT 1 corresponds to a firstemitter-collector resistor 32. The resistor between emitter terminal 20and second collector terminal 40 of first LMT 1 corresponds to a secondemitter-collector resistor 42. In addition, the resistor between emitter21 and first collector terminal 31 of second LMT 2 corresponds to athird emitter-collector resistor 33. In addition, the resistor betweenemitter terminal 21 and second collector terminal 41 of second LMT 2corresponds to a fourth emitter-collector resistor 43. In the presenceof an external magnetic field 14 lateral to the chip surface, thecurrent distributions between first collector 30, 31 and secondcollector 40, 41 change in both LMTs 1, 2. This corresponds to aresistance change of the collector-emitter paths 32, 42, 33, 43 in FIG.3. Depending on the application, the two complementary LMTs 1, 2 are tobe suitably aligned with the magnetic field 14 to be measured. Theeffect of the magnetic field 14 on resistance measuring bridge 80 may beselected depending on the application via the relative position ofcomplementary LMTs 1, 2, for example, via the chip layout or by usingsuitable electric linking of collectors 30, 40 or 31, 41.

If the electrical connection of insulated npn type and pnp type LMTs 1,2 is not produced by bonding wires, lead frames, flex film, etc. untilafter the chip is produced, it is then possible, for example, tomanufacture a universal sensor element, whose measuring bridge isconnected later, corresponding to the conditions of use. Alsoconceivable is a chip having several differently aligned npn type andpnp type LMT elements, two of which, for example, are selected andconnected to form a suitable measuring bridge as a function of theapplication requirement.

Since at least two LMT sensors 1, 2 are involved in the bridge circuit,it is possible to implement different measuring methods. Both LMTelements 1, 2 may be arranged in such a way that they are exposed to thesame magnetic field 14, as a result of which the effect of the field isadditive. However, the sensors may also be placed in such a way thatthey “see,” i.e., detect different magnetic fields, for example, for adifferential or a reference measurement. Depending on the application,therefore, it is possible to use the bridge circuit of the presentinvention in a very flexible manner.

High standards for precision and resolution set similarly high standardsfor stability and the balancing of the zero point offset of a sensor.The present high-precision measuring bridge arrangement is suited forprecise balancing requirements in a particularly advantageous manner. Inaddition, the offset and the temperature drift may be compensated in arelatively simple manner by a slight adaptation of the working point ofone of the four collector-emitter paths 32, 42, 33, 43.

According to the present invention, LMT components having no substratecollector 7 are also used in the present device.

According to the invention, the device of the present invention isprovided in particular as a magnetic field meter, such a magnetic fieldmeter including not only the described device made up of the two LMTs1,2 but also an evaluation circuit or a trigger circuit.

In addition, a highly sensitive magnetic field detector or magneticfield meter or the device of the present invention may be used forcurrent measurement, by measuring the magnetic field effect around acurrent-carrying conductor being used.

1. A device for detecting a magnetic field, comprising: a first lateralmagnetotransistor; and a second lateral magnetotransistor, wherein thefirst and second lateral magnetotransistors are complementary.
 2. Thedevice of claim 1, wherein the first lateral magnetotransistor is npntype and the second lateral magnetotransistor is pnp type.
 3. The deviceof claim 1, wherein the first lateral magnetotransistor has a firstoutput and a second output, the second complementary lateralmagnetotransistor has a third output and a fourth output, and whereinthe first output and the third output are connected via low resistance,the second output and the fourth output are connected via lowresistance, and wherein a measuring bridge is provided between the firstoutput and the fourth output.
 4. The device of claim 3, wherein thefirst output and the third output are complementary, and wherein thesecond output and the fourth output are complementary.
 5. The device ofclaim 4, wherein the first output and the second output are collectorterminals of the first lateral magnetotransistor, and wherein the thirdoutput and the fourth output are collector terminals of the secondlateral magnetotransistor.
 6. The device of claim 3, wherein the firstoutput and the second output are collector terminals of the firstlateral magnetotransistor, and wherein the third output and the fourthoutput are collector terminals of the second lateral magnetotransistor.7. The device of claim 1, wherein the first lateral magnetotransistorand the second lateral magnetotransistor are monolithically integrated.8. The device of claim 1, wherein the device is for use in a magneticfield meter.
 9. The device of claim 8, wherein the magnetic field meterincorporating the device is in turn incorporated in an ammeter.
 10. Thedevice of claim 1, wherein the device is for use in an ammeter.